A variety of harmful heavy metal ions are contained in some industrial waste water and must be removed by waste water treatment as much as possible in view of the prevention of environmental pollution. Since many of such harmful heavy metal ions can be effectively used, for example, as useful metals, it serves as a double purpose to separate and recover these ions and use these ions effectively as secondary resources.
Ion exchange resins have been widely used for removing harmful heavy metal ions and for capturing useful metal ions contained in, for example, water before or after use. However, the ion exchange resins cannot always have sufficient effects of selectively adsorbing low concentration metal ions.
Chelate resins capable of forming a chelate with metal ions to thereby selectively capture these metal ions have excellent capability of selectively capturing metal ions, especially of caputring heavy metal ions, thus the chelate resins are used to remove or capture heavy metals in the field of water treatment.
However, since most of the chelate resins are bead-like resins having a rigid three-dimensional crosslinked structure formed by action of a crosslinking agent such as divinylbenzene and are hydrophobic, a rate of diffusion and permeation of metal ions or regenerants into the resins is lowered. Thus, treatment efficiency is insufficient. In addition, in the case of disposal of the used resins without being regenerated, problems such as difficulty in incineration and complicated volume reduction of the used resins have been greatly pointed out.
As a possible solution to these problems of bead-like chelatable resins, a fibrous chelate resin has been proposed (e.g., Japanese Patent No. 2,772,010). This fibrous chelate resin has a large specific surface area, includes a chelatable functional group, by which metal ions are adsorbed or desorbed on its surface, and therefore has an improved adsorption and desorption capability.
However, the fibrous chelate resin comprises a polymer of an olefin or halogenated olefin as a base, and invites the formation of dioxins or other harmful gases when it is incinerated. Additionally, a process for producing the fibrous chelate resin, namely modification to impart metal chelating activity to a resin, is complicated and requires a special process using, for example, ionizing radiation, and a number of disadvantages have been pointed out in terms of, for example, facilities, safety, and production cost.
The present invention has been accomplished under these circumstances, and a first object of the present invention is to provide a metal chelate forming fiber that has satisfactory capturing property for harmful heavy metal ions, can be easily discarded and incinerated, moreover, can be produced at low cost in a simple and safe manner. It is a second object of the invention to provide a process for easily, safely, and efficiently producing the metal chelate forming fiber.
A third object of the present invention is to provide a method of easily and efficiently capturing metal ions contained in trace amounts, for example, in an aqueous or oily liquid or in a gas such as an exhaust gas and the like by the use of the metal chelate forming fiber. Additionally, a fourth object of the present invention is to provide a metal chelate fiber which is making use of catalytic activities or antimicrobial activities of a variety of metals by allowing the metals to be bonded by chelation to a surface of the metal chelate forming fiber.